For over a decade, the military has been devoting a large amount of research and development funding to research projects directed to reducing the impact and shock sensitivity of the main explosive charge in munitions. A main challenge is to reduce sensitivity of the main explosive charge without decreasing performance while also not significantly increasing cost. One of the main charge explosives in munitions formulations is a caged nitramine compound. The chemical name of the compound is 2,4,6,8,10,12-hexanitrohexaazoisonurtitane (CL-20). The only known practical way to reduce the sensitivity of these formulations is to increase the amount of inerts and less sensitive components therein and thus decrease the sensitivity of the formulation but this also reduces the performance of the formulation. Further, extensive discussion of this problem is set forth in U.S. Pat. No. 4,842,659. In this patent it is stated that insensitive munitions must be developed to improve the combat survivability of an armament vehicle. It has been found that munitions utilized in some weapon systems are vulnerable to sympathetic detonation. For instance, the cannon caliber ammunition stored aboard these vehicles is vulnerable to initiation via shape charge jet and then propagation of the reaction due to sympathetic detonation.
This sympathetic detonation and propagation scenario can be summarized as follows: If a round is hit by a shape charge jet, it is initiated. As a result, the fragments that are generated by the blast then strike the other rounds that are adjacent to it. The latter rounds then initiate, contributing to the overall reaction and damage sustained by the vehicle, crew, and other munitions. The mechanisms of reaction for the initiation of the surrounding rounds are due to the blast and fragments impinging on the aforesaid adjacent round. The probability of sympathetic detonation can be reduced in several ways. This can be done by reconfiguring the ammunition compartments within the vehicle. It can also be accomplished by packaging the ammunition with anti-fratricide materials. However, each of the aforesaid solutions will reduce the amount of space available for the storage of ammunition. The most acceptable solution to the problem is to reduce the sensitivity of the energetic material to sympathetic detonation. Incorporating less sensitive energetic material will reduce the vulnerability of initiation from the cited threats without reducing the number of rounds stored in the vehicle. It has been found that by reducing the vulnerability to sympathetic detonation of the energetic materials used in these munitions, the probability of catastrophic reaction can be minimized.
The mechanism generally accepted within the explosives community for detonating or deflagrating explosives is the creation of very localized regions of high temperature, i.e., hot spots. The application of impact or shock on the explosive can generate hot spots in the following ways: (1) by adiabaticly compressing air (or explosive vapor) bubbles trapped in or purposely introduced into the explosive, (2) by intercrystalline friction, (3) by friction of the impacting surfaces, (4) by plastic deformation of a sharply-pointed impacting surface, and (5) by viscous heating of the impacted material as it flows past the periphery of the impacting surfaces.
In the compression and movement of explosive crystals due to impact or shock, explosives like CL-20 rapidly evolve into simpler products as well as free radicals and unstable intermediates. This mixture of products is believed to be unstable and subject to detonation when exposed to a low intensity shock induced spark of static electricity. The creation and build-up of static electricity may be an additional source of energy which contributes to the detonation of the explosive and its decomposition products.